Induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) have the potential to provide a relevant platform for basic research and drug development. The advantages of these cells over current in vitro models used to investigate the effect of a drug on electrical activity are that they are of human origin and can be derived directly from the target patient population. However, one major obstacle to using iPSC-CMs is that they possess an immature phenotype, making it difficult to determine if resulting behavior reflects adult cardiomyocyte behavior. It has been demonstrated that a missing inward rectifier potassium current, IK1, can be artificially re-introduced via ?dynamic clamp?, an electrophysiological technique that allows for control of electrical input based on real-time feedback and analysis of membrane potential. This approach makes iPSC-CMs more electrophysiologically adult-like, enabling the investigation of the effect of drugs on action potential morphology and kinetics. However, this method is tedious, low throughput, and can only be performed on single cells. We aim to improve upon this approach by applying optogenetic techniques in combination with optical mapping in iPSC-CM beating clusters to create a novel ?optical dynamic clamp? platform for screening. Key points: ? The design of the optical dynamic clamp will be based on the same principles of traditional dynamic clamp. ? ArchT, a hyperpolarizing optogenetic proton pump, will be used to artificially compensate for the missing IK1 component in the beating clusters of iPSC-CMs and push its electrical maturity. ? Optical mapping with voltage sensitive dyes will be used to extract information on action potential morphology and kinetics as well as provide the necessary real-time information to control the dynamic system. ? This platform does not restrict us to using only single cells, but allows for the use of beating clusters of iPSC-CMs. Beating clusters offers the advantage of being more tissue-like since individual cardiomyocytes will be electrically coupled to its neighbors, similarly to in vivo conditions. Importantly, the optical nature of the approach (in contrast to patch clamping) will enable high- throughput drug screening using iPSC-CMs in a more tissue-like format of cells, allowing for more meaningful interpretations of disease and drug mechanisms of action.